A few inches of wet snow can weigh more on a roof than a much deeper layer of dry powder. There’s no single inches-based answer to how much snow a roof in Spokane Valley can handle.
Snow weight, drifting, ice buildup, the roof’s condition, and the structure below it all matter. A close look at the roof is more useful than trying to judge safety from the ground.
Start with the Roof’s Design Load, Not Snow Depth
Spokane County guidance lists 30 pounds per square foot as the basic minimum roof snow load. This is the weight a roof is designed to support across each square foot of its surface, not a recommended amount of snow to leave in place.
The City of Spokane uses 39 pounds per square foot for snow on the ground and a 30 pounds per square foot minimum for roofs. The ground figure reflects snow weight measured at ground level, while the roof requirement accounts for how snow affects the building itself.
Those figures provide useful local context, but they aren’t a universal safety threshold for every existing roof. Some Spokane County locations require design loads as high as 150 pounds per square foot. A building’s age, elevation, construction, alterations, and current condition also affect its capacity.
Understanding a particular roof’s capacity starts with its design history, not a ruler. Original building documents or an evaluation by a qualified structural professional are reliable sources for its intended design.
Why Snow Depth Doesn’t Tell You the Whole Story
Snow density, meaning how much a given volume weighs, changes dramatically with weather conditions. Estimates in pounds per cubic foot include:
- Fresh snow: about 3.75.
- Settled snow: about 15.61.
- Very wet snow: about 46.82.
- Ice: about 57.25.
A simple screening formula multiplies snow density by depth in feet. For example, 6 inches of very wet snow is half a foot deep, so 46.82 multiplied by 0.5 equals about 23.41 pounds per square foot. This estimate doesn’t account for roof pitch, drifting, or the building’s structure, so it shouldn’t be treated as a structural determination.
Rain, compaction, thawing, and refreezing add weight without always making the layer look much deeper. After several changing weather cycles, a roof can carry more weight than it did immediately after a larger but lighter snowfall.
Watch for Uneven Snow Accumulation
Snow drifts can hold two to three times more snow than nearby areas with level-looking coverage. This creates concentrated stress rather than an even load.
Pay particular attention to places where wind and roof geometry direct snow:
- Beside taller walls, chimneys, parapets, and other obstructions.
- At roof transitions, valleys, lower roof sections, and areas below upper stories.
- Along eaves and shaded areas where ice can hold snow in place.
Spokane’s record snowfall of December 2008, which led into a wave of roof collapses in early January 2009, showed why roof condition matters as much as a code figure. Numerous Inland Northwest roof collapses occurred while the official reading reached 28.6 pounds per square foot, below the 30 pounds per square foot minimum. Deteriorated or substandard construction can leave a roof vulnerable before a local code baseline is reached.
Roof pitch also matters. A steeper roof generally sheds snow more readily, while low-slope areas, valleys, and flat-roof sections tend to retain it. Prior leaks, damaged decking or supports, and drainage problems deserve attention before winter accumulation becomes heavy.
Warning Signs That Need Prompt Attention
Visible movement, new interior damage, or unusual sounds can indicate that the roof or its support system needs prompt assessment. Snow itself isn’t always the problem, but a changing roof can be.
Take the following signs seriously:
- New sagging in the roofline, ceiling, or attic framing.
- Cracks or shifting in ceilings, walls, or interior finishes.
- Unusual creaking, popping, or cracking sounds from above.
- Doors or windows that suddenly bind or no longer close normally.
- New leaks, stained ceilings, or water entering around roof penetrations.
Don’t climb onto a snow-covered roof to investigate or remove snow if there’s a fall hazard or any sign of structural stress. If the roof appears to be sagging significantly, move people away from the affected area and seek emergency help if collapse appears possible.
Ice dams deserve attention even when accumulation is light. An ice dam forms when meltwater refreezes near the roof edge, trapping water behind it. Freeze-thaw cycles can contribute to cracked shingles, moisture retention in roof decking, and leaks inside the building.
What a Roof Inspection Can Clarify
A roof inspection can document visible conditions relevant to winter concerns:
- Storm damage.
- Areas prone to uneven accumulation.
- Drainage issues.
- Ice-dam indicators.
- Signs of moisture intrusion.
An inspection doesn’t replace a structural engineering evaluation when there’s building movement or a possible structural failure.
When we inspect a roof, we take measurements, assess its condition, and document our findings with discovery photos before preparing an estimate. This gives property owners a clearer basis for deciding whether the concern calls for monitoring, storm-related mitigation, or planning for a full roof replacement.
Don’t rely on a universal inches-of-snow rule. Focus on whether the accumulation is uneven or growing heavier and whether the building shows signs of distress.
At Apex Roofing, we provide free roof inspections and storm-related support in Spokane Valley. Reach our team at (877) 939-9866 to discuss what you’re seeing.